The milky white stone is made of Iceland spar, a transparent calcite crystal that polarizes light and can get a bearing on the sun.

The Vikings are said to have used such crystals to tell where the sun was on cloudy days before magnetic compasses, according to History.com.

If the discovery is valid, it could be one of the secrets behind the Vikings' reputation as remarkable seafarers and explain how they may have beaten Christopher Columbus in visiting America, according to The Indepdndent.

In a study published in the British journal Proceedings of the Royal Society, investigators confirmed the stone was a calcite through testing and were able to follow the track of the sun using a similar stone with an accuracy of 1 degree.